Vacuum tube for accelerating charged particles, such as electrons or ions, by high electric direct voltages

ABSTRACT

An acceleration tube for accelerating charged particles by high electric direct voltage with a plural stage immersion optic system, in which the vacuum vessel comprises a preferably cylindrical undivided glass or ceramic tube closed at both ends by detachable flanges. The immersion optic system includes metallically conductive optic elements, insulating spacer and connecting members, and voltage dividing resistor chain means for distributing the potential in conformity with the respective requirements among said individual optic elements, said immersion optic system being adapted after disengagement of one of said flanges to be removed from and to be installed in said vessel as an entirety.

United States Patent [191 Willutzki Nov. 6, 1973 [22] Filed: June 5, 1972 [21] Appl. No.: 259,587

[30] Foreign Application Priority Data June 4, 1971 Germany ..P 21 2 769l1 [52] US. Cl 313/63, 315/46, 315/59 [5 1] Int. Cl. H05h 5/00 [58] Field of Search 313/63; 315/46, 59

Primary Examiner-Roy Lake Assistant Examiner-Darwin R. Hostetter Att0rney-Walter Becker 5 7'] ABSTRACT An acceleration tube for accelerating charged particles by high electric direct voltage with a plural stage immersion optic system, in which the vacuum vessel comprises a preferably cylindrical undivided glass or ceramic tube closed at both ends by detachable flanges. The immersion optic system includes metallically conductive optic elements, insulating spacer and connecting members, and voltage dividing resistor chain means for distributing the potential in conformity with the respective requirements among said individual optic elements, said immersion optic system being adapted after disengagement of one of said flanges to be removed from and to be installed in said vessel as an entirety.

7 Claims, 2 Drawing Figures SOURCE OF PARTICLES TO BE ACCELERATED Va :vu m Pu p PATENTEDHQY 6 1973 3,771,000

SOURCE OF PARTIC TO BE ACCELER n VACUUM TUBE FOR ACCELERATING CHARGED PARTICLES, SUCH AS ELECTRONS OR IONS, BY HIGH ELECTRIC DIRECT VOLTAGES The present invention relates to a vacuum tube for accelerating charged particles, such as electrons and ions, by high electric direct voltages.

High accelerating voltages require a considerable length of the insulating portion of the tube wall because the materials, silicate glass and ceramics, exclusively employed at this place in view of their sufficiently low steam pressure, have an unfavorable surface behavior with the tendency to bring about sliding discharges (Gleitentladungen), especially when at the vacuum side there occur additional partial charges by electrons and conductive layers by ions.

From some hundred kilovolt upwards up to the meg avolt range, it is expedient to effect the particle acceleration in a plurality of serially arranged stages (cascade acceleration) and to bundle the particles which divergently leave the particle source. Such bundling is advisable particularly when the purpose of employment of the accelerating tube makes necessary the projection of the particle source in a definite plane and at a definite projection scale. An arrangement which simultaneously solves both problems, namely the multistage acceleration as well as the bundling of the diverging particle beam or the projection of the particle source, is a multistage electrostatic immersion optic. Such optic comprises a plurality of metal electrodes of a diaphragm or anode aperture character which are arranged coaxially with regard to the tube axis and are evenly spaced from each other while therebetween the acceleration voltage is divided at equal stages. The metallic optic electrodes are in most instances so designed, for instance by a conical deformation of the axis-near range in the particle flight direction, that secondary and stray electrons as well as ions will be able to reach the insulating tube wall only to a minor extent. The assembly of such cascade acceleration tubes is so effected that the metallic electrodes are alternately cemented coaxially with the spacer rings of smaller diameter consisting of glass or ceramic in such a way that these spacer rings will then form the insulating wall of the vacuum vessel. This design of the cascade acceleration tubes as it is at present customary makes it possible to feed the necessary voltage to the optic electrodes which are accessible outside the vacuum chamber, which voltages are necessary for the functioning of the electrodes. This customary design, however, has considerable defects with regard to the manufacturing and application techniques:

a. The building elements optic electrodes and spacer rings require considerable machining in the region of the cementing grooves; in particular the glass and ceramic spacer rings have to be ground plane parallel at the end faces because these ground surfaces determine not only the tightness of the cementing grooves but also the adjustment of the optics.

b. The considerable total length of the cementing grooves is undesired from a vacuum technical standpoint inasmuch as the employable cements in most instances have a relatively high vapor pressure.

0. The unfavorable field distribution within the region of the cementing grooves as well as the cation emission thereof cause slip discharges on the spacer rings.

d. The different heat expansion coefficient of optic electrodes and spacer rings causes leakages and even breakage of the briddle spacer rings.

e. A post-adjusting of the optics is not possible.

It is, therefore, an object of the present invention to provide an acceleration tube for charged particles by high electric direct voltage with multi-stage immersion optics, which will overcome the drawbacks outlined above under (a) (e).

This object and other objects and advantages of the invention will appear more clearly from the following specification in connection with the accompanying drawing, in which: 3

FIG. 1 is a longitudinal section through an acceleration tube according to the invention.

FIG. 2 is a transverse section taken along the line II II of FIG. 1.

The vacuum vessel according to the present invention, instead of consisting of individual insulating spacer rings with interposed and cemented-in optical elements, comprises a non-divided preferably cylindrical glass or ceramic tube 1 which is closed at both ends by detachable flanges 2, 3. Flange 2 has a tubular connection 8 which comprises the source of the particles to be accelerated. The flange 3 is connected to a vacuum pump. In view of this arrangement all drawbacks listed above under (a) (d) and caused by metal glas or metal ceramic cementing are eliminated.

The metallic immersion optic elements 4 form together with the insulating spacer and connecting members 5 and the separately disconnectable voltage dividing resistors 6 the immersion optic system which, as will be seen from the drawing, can now be installed and removed as a unit, particularly when it is firmly connected to the upper flange. The adjustment of the optic elements may with this arrangement be effected outside the vacuum vessel. A post-adjustment, an exchange of defective voltage distributing resistors as well as a cleaning of the inner tube wall is possible at all times at low costs. The helical resistor chain 7 wound around the tube has the purpose of assuring a substantially uniform field distribution in the direction of the acceleration field which uniform field distribution is very important for the dielectric strength of the entire arrangement. Inasmuch as the here provided immer sion optics are not variable, while it sometimes may be necessary to vary the projection ratio of particle source focal spot, there is provided a variable magnetic lens between the particle source and the first immersion optic element, in other words, where the particles are relatively slow and therefore are easily influened.

It is, of course, to be understood that the present invention is, by no means, limited to the particular showing in the drawing but also comprises any modifications within the scope of the appended claims.

What I claim is:

1. An acceleration tube for accelerating charged particles by high electric direct voltage, which includes: a single piece tubular vacuum'vessel of electrically insulating material open at both ends; flange means respectively detachably connected to the end portions of said vessel for selectively closing said open ends; and a plural stage immersion optic system arranged within said vessel and comprising metallically conductive optic elements, insulating spacer and connecting elements, and voltage dividing resistor chain means for distributing the respective potential among the individual optic elements; said voltage dividing resistor chain means being arranged in parallel with regard to the flow of the charged particles to be accelerated, and said immersion optic system being adapted after detachment of one of said flange means selectively to be withdrawn from and installed in said vessel as an entirety forming a single unit.

2. An acceleration tube according to claim 1, in which said vacuum vessel is of glass.

3. An acceleration tube according to claim 1, in which said vacuum vessel is of ceramic material.

4. An acceleration tube according to claim 1, in which said tubular vacuum vessel is cylindrical.

5. An acceleration tube according to claim 1, which includes a resistor chain in the form of a coil arranged in parallel with regard to the flow of particles to be accelerated and surrounding said vacuum vessel, said resistor chain being so arranged that the distribution of the potential on the outside wall surface of said vessel is at least nearly identical to that on the inside wall surface of said vessel.

6. An acceleration tube according to claim 1, which includes housing means connected to one of said flange means and adapted to receive and serve as source of the charged particles to be accelerated, and a variable magnet lens interposed between said housing means and the respective nearest one of said optic elements, said magnet lens being substantially coaxial with regard to said immersion optic system.

7. An acceleration tube according to claim 1, which includes: housing means connected to one of said flange means and adapted to receive and serve as source of the charged particles to be accelerated, said immersion optic system having one end portion firmly connected to that flange means to which said housing means is connected, and movable guiding means connecting the other end of immersion optic system with the other flange means, said guiding means being movable in the axial direction of said tubular vessel. 

1. An acceleration tube for accelerating charged particles by high electric direct voltage, which includes: a single piece tubular vacuum vessel of electrically insulating material open at both ends; flange means respectively detachably connected to the end portions of said vessel for selectively closing said open ends; and a plural stage immersion optic system arranged within said vessel and comprising metallically conductive optic elements, insulating spacer and connecting elements, and voltage dividing resistor chain means for distributing the respective potential among the individual optic elements; said voltage dividing resistor chain means being arranged in parallel with regard to the flow of the charged particles to be accelerated, and said immersion optic system being adapted after detachment of one of said flange means selectively to be withdrawn from and installed in said vessel as an entirety forming a single unit.
 2. An acceleration tube according to claim 1, in which said vacuum vessel is of glass.
 3. An acceleration tube according to claim 1, in which said vacuum vessel is of ceramic material.
 4. An acceleration tube according to claim 1, in which said tubular vacuum vessel is cylindrical.
 5. An acceleration tube according to claim 1, which includes a resistor chain in the form of a coil arranged in parallel with regard to the flow of particles to be accelerated and surrounding said vacuum vessel, said resistor chain being so arranged that the distribution of the potential on the outside wall surface of said vessel is at least nearly identical to that on the inside wall surface of said vessel.
 6. An acceleration tube according to claim 1, which includes housing means connected to one of said flange means and adapted to receive and serve as source of the charged particles to be accelerated, and a variable magnet lens interposed between said housing means and the respective nearest one of said optic elements, said magnet lens being substantially coaxial with regard to said immersion optic system.
 7. An acceleration tube according to claim 1, which includes: housing means connected to one of said flange means and adapted to receive and serve as source of the charged particles to be accelerated, said immersion optic system having one end portion firmly connected to that flange means to which said housing means is connected, and movable guiding means connecting the other end of immersion optic system with the other flange means, said guiding means being movable in the axial direction of said tubular vessel. 